Image sensor and method for manufacturing the same

ABSTRACT

In a solid state imaging device, and a method of manufacture thereof, the efficiency of the transfer of available photons to the photo-receiving elements is increased beyond that which is currently available. Enhanced anti-reflection layer configurations, and methods of manufacture thereof, are provided that allow for such increased efficiency. They are applicable to contemporary imaging devices, such as charge-coupled devices (CCDs) and CMOS image sensors (CISs). In one embodiment, a photosensitive device is formed in a semiconductor substrate. The photosensitive device includes a photosensitive region. An anti-reflection layer comprising silicon oxynitride is formed on the photosensitive region. The silicon oxynitride layer is heat treated to increase a refractive index of the silicon oxynitride layer, and to thereby decrease reflectivity of incident light at the junction of the photosensitive region.

RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.2004-49001, filed on Jun. 28, 2004, the disclosure of which is herebyincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

Solid-state imaging devices enjoy widespread use in contemporary imagingsystems. Popular solid-state imaging devices include charge-coupleddevices (CCD) and CMOS image sensors (CIS). Such devices are commonlyemployed in digital still cameras, digital video cameras, cellulartelephones, and security systems.

The solid state imaging device converts transmitted light in the form ofphoton energy to electrical signals, and the electrical signals areconverted to information that can be presented on display devices orotherwise processed by a computer system. CCD and CIS imaging devicesinclude photo-reception elements such as photodiodes. Therefore, asignificant factor in the efficiency and efficacy of such devices is theability of the photo-reception elements to convert available photons toelectrons. If the photon count being transmitted to the photo-receptionelements is less than a threshold amount, the information presented onthe display is adversely affected.

FIG. 1 is a sectional view of a conventional solid state imaging device.An n type photodiode device region 12 is formed in a substrate 10. A p+doped region 14 is formed in the substrate 10 adjacent the photodiodedevice region 12. The p+ doped region 14 operates as a channel stopregion, or insulative region, to prevent the flow of electrons betweenadjacent imaging devices on the substrate. A gate dielectric layer 16comprising SiO₂ or oxide-nitride-oxide (ONO) and a polysilicon transfergate layer 18 are then formed on the substrate 10 and patterned toexpose the photodiode device. region 12 and to thereby form a transfergate structure at side regions of the photodiode device region 12.

An anti-reflection layer 30 is formed on the resulting structure. Across-sectional close-up view of an anti-reflection layer is shown inFIG. 2. The anti-reflection layer 30 includes a first dielectric layer31 comprising silicon dioxide and a second dielectric layer 33comprising silicon nitride. The anti-reflection layer 30 reduces thenumber of reflected photons that are incident on the photodiode device12, and therefore leads to improved efficiency in thephoton-to-electrical energy transfer. Absent an anti-reflection layer30, the reflectivity of photon energy at the surface of the photodiodedevice region 12 is on the order of 20%-30%. The presence of theconventional anti-reflection layer 30 shown in FIGS. 1 and 2 improvesthe reflectance level to a reduced amount on the order of 10%-20%.Returning to FIG. 1, a buffer layer 36 comprising silicon dioxide isformed over the top of the second dielectric layer 33 of theanti-reflection layer.

A protective shield layer 60 comprising tungsten is layered over theresulting structure, and is patterned to expose the anti-reflectionlayer 30 and buffer layer 36 in the photodiode device region 12. Theprotective shield layer 60 prevents photon energy from directly enteringthe transfer gate 18. A planarization layer 62 comprising silicondioxide is then provided on the resulting structure and planarized, forexample using chemical-mechanical polishing (CMP). A microlens 64 formedof resin is formed on the top of the planarization layer 62.

With the trend toward ever-increasing integration of solid state imagingdevices, compact design and increased pixel density are of primaryconcern. With these goals in mind, the amount of light available at thelight-receiving region of the device has been reduced, due to thereduced device size, thereby limiting device sensitivity. To improvesensitivity, the microlens 64 is provided to focus the incident lightinto the photodiode device region 12. At the same time, theanti-reflection layer 30 reduces the amount of reflected light andtherefore enhances the capture of light energy at the photodiode deviceregion 12.

Japanese patent publication JP 2003-224250 provides an example of adouble-layered anti-reflection layer comprising a sequentially formedstructure as follows: first silicon dioxide layer/first silicon nitridelayer/second silicon dioxide layer/second silicon nitride layer. Eachcombined silicon dioxide/silicon nitride layer pair forms oneanti-reflection layer. This configuration provides for further reducedreflectivity as compared to the single anti-reflection layerconfiguration of FIG. 2

FIG. 3 is an experimental graph illustrating reflectance as a functionof the wavelength of light as a result of the application of first andsecond anti-reflection layers of the double-layered embodiment of JP2003-224250. It can be seen in this graph that the application of thesecond anti-reflection layer operates to reduce reflectance in thevisible light wavelength region of about 500-700 nm, as compared to thesingle reflection layer. However, the reflectance level of thedouble-layered configuration is actually higher than the single-layeredconfiguration in approximately the 400 -500 nm wavelength region, andthe double-layered configuration still demonstrates at least 4%reflectance in the visible wavelengths, an amount that can be limitingto device effectiveness as device integration continues.

SUMMARY OF THE INVENTION

The present invention is directed to a solid state imaging device, and amethod of manufacture thereof, which increases the efficiency of thetransfer of available photons to the photo-receiving elements beyondthat which is currently available. The enhanced anti-reflection layerconfigurations, and methods of manufacture thereof, of the presentinvention, provide for such increased efficiency, and are applicable tocontemporary imaging devices, such as charge-coupled devices (CCDs) andCMOS image sensors (CISs).

In a first aspect, the present invention is directed to a method offorming an imaging device. A photosensitive device is formed in asemiconductor substrate. The photosensitive device includes aphotosensitive region. An anti-reflection layer is formed on thephotosensitive region. The anti-reflection layer comprises a siliconoxynitride layer. The silicon oxynitride layer is heat treated toincrease a refractive index of the silicon oxynitride layer.

In one embodiment, forming a photosensitive device comprises forming acharge-coupled device (CCD). In this case, forming a charge-coupleddevice comprises: forming a charge transfer region in the substrateadjacent the photosensitive region; and forming a transfer gate abovethe transfer region. In addition, an insulative capping layer is formedon the anti-refection layer, a shielding layer is formed on the cappinglayer between side portions of the anti-reflection layer and thetransfer gate; and a planarization layer is formed on the shieldinglayer and capping layer.

In another embodiment, the method further comprises forming an innerlens in the planarization layer, forming a microlens on theplanarization layer, and/or forming a color filter layer on theplanarization layer.

In another embodiment, forming a photosensitive device comprises forminga CMOS image sensor (CIS) device, which, in turn, comprises: forming acharge transfer region in the substrate adjacent the photosensitiveregion; forming a floating diffusion region adjacent the charge transferregion opposite the photosensitive region; and forming a transfer gateabove the charge transfer region. In addition, a dielectric layer isformed on the anti-refection layer, metal interconnects are formed inthe dielectric layer; and metal vias are formed through the dielectriclayer to connect first and second metal interconnects with the transfergate and with the floating diffusion region respectively. Forming thedielectric layer comprises forming multiple dielectric layers, andforming metal interconnects comprises forming metal interconnects at topportions of the multiple dielectric layers. The method further comprisesforming an inner lens on the dielectric layer, forming a planarizationlayer on the inner lens and forming a microlens on the planarizationlayer, and/or forming a color filter layer on the planarization layer.

In another embodiment, the method further comprises forming a holeaccumulation layer (HAL) at a top portion of the photosensitive region.

In another embodiment, forming the anti-reflection layer comprises:forming a first silicon dioxide layer on the photosensitive region, andforming the silicon oxynitride layer on the first silicon dioxide layer.Forming the first silicon dioxide layer comprises depositing the firstsilicon dioxide layer on the photosensitive region using one of a lowpressure chemical vapor deposition (LPCVD) process and an Atomic LayerDeposition (ALD) process. Forming the silicon oxynitride layer comprisesdepositing the silicon oxynitride layer on the first silicon dioxidelayer using plasma enhanced chemical vapor deposition (PECVD). Formingthe silicon oxynitride layer comprises depositing the silicon oxynitridelayer using plasma enhanced chemical vapor deposition (PECVD) to athickness of about 20 to 60 nm.

In another embodiment, forming the anti-reflection layer furthercomprises: forming a second silicon dioxide layer on the siliconoxynitride layer and forming a silicon nitride layer on the secondsilicon dioxide layer. Forming the second silicon dioxide layercomprises depositing the second silicon dioxide layer on thephotosensitive region using a chemical vapor deposition (CVD) process,and forming the silicon nitride layer comprises depositing the siliconnitride layer on the second silicon dioxide layer using a CVD processthat uses source gases of SiH₄, N₂O, and/or NH₃ in an environment ofnitrogen.

Heat treating the silicon oxynitride layer increases the refractiveindex of the silicon oxynitride layer to an amount ranging between about2.3 and 3.0.

In another embodiment, the method further comprises patterning theanti-reflection layer in a region above the photosensitive layer byproviding a photoresist layer on the anti-reflection layer; patterningthe photoresist layer above the photosensitive region; and removing thesilicon oxynitride layer of the anti-reflection layer using thepatterned photoresist layer as a mask. Alternatively, patterning theanti-reflection layer comprises: providing a hard mask layer on theanti-reflection layer; patterning the hard mask layer above thephotosensitive region; and removing the silicon oxynitride layer of theanti-reflection layer using the patterned hard mask layer as a mask.

Removing the silicon oxynitride layer of the anti-reflection layercomprises removing the silicon oxynitride layer using an HF solution.

Forming the anti-reflection layer comprising the silicon oxynitridelayer comprises forming the silicon oxynitride layer using plasma-basedchemical vapor deposition (CVD). In one embodiment, the plasma-basedchemical vapor deposition comprises plasma enhanced chemical vapordeposition (PECVD). Heat treating the silicon oxynitride layer increasesthe refractive index of the silicon oxynitride layer to an amountranging between about 2.3 and 3.0. Heat treating the silicon oxynitridelayer comprises heat treating at a temperature greater than about 600 C,and/or for a time duration ranging between about 30 and 360 minutes.

The heat treating of the silicon oxynitride layer increases therefractive index of the silicon oxynitride layer to an amount rangingbetween about 2.3 and 3.0. Heat treating of the silicon oxynitride layercan be performed immediately following formation of the siliconoxynitride layer, or during further processing of the imaging device.

In another aspect, the present invention is directed to a method offorming an imaging device. A photosensitive device is formed in asemiconductor substrate; the photosensitive device including aphotosensitive region. An anti-reflection layer is formed on thephotosensitive region that reduces the reflectivity of photon energy atthe photosensitive device. The anti-reflection layer includes a siliconoxynitride layer and has a refractive index ranging between about 2.3and 3.0.

In one embodiment, forming the anti-reflection layer comprises: formingthe anti-reflection layer proximal to the photosensitive device so thatthe anti reflection layer has a refractive index of about 2.0; and heattreating the silicon oxynitride layer to increase the refractive indexof the silicon oxynitride layer to range between about 2.3 and 3.0.

In another aspect, the present invention is directed to a method offorming a semiconductor image sensor. A photosensitive device includinga photosensitive region is formed in a semiconductor substrate. Ananti-reflection layer is formed on and proximal to the photosensitiveregion for reducing reflection at a top interface of the photosensitiveregion. The anti-reflection layer includes a silicon oxynitride layer.

In one embodiment, forming the anti-reflection layer comprises formingthe anti-reflection layer to have a refractive index ranging betweenabout 2.3 and 3.0 by: forming the anti-reflection layer proximal to thephotosensitive device so that the anti reflection layer has a refractiveindex of about 2.0; and heat treating the silicon oxynitride layer toincrease the refractive index of the silicon oxynitride layer to rangebetween about 2.3 and 3.0.

In another aspect, the present invention is directed to a method offorming a semiconductor image sensor. A photosensitive device includinga photosensitive region is formed in a semiconductor substrate. Ananti-reflection layer is formed on and proximal to the photosensitiveregion for reducing reflection at a top interface of the photosensitiveregion, the anti-reflection layer having a refractive index rangingbetween about 2.3 and 3.0.

In one embodiment, forming the anti-reflection layer comprises formingthe anti-reflection layer to include a silicon oxynitride layer. Theanti-reflection layer is formed proximal to the photosensitive device sothat the anti reflection layer has a refractive index of about 2.0; andthe silicon oxynitride layer is heat treated to increase the refractiveindex of the silicon oxynitride layer to range between about 2.3 and3.0.

In another aspect of the present invention is directed to asemiconductor image sensor. The sensor includes a photosensitive deviceincluding a photosensitive region formed in a semiconductor substrate;and an anti-reflection layer proximal to the photosensitive region forreducing reflection at a top interface of the photosensitive region. Theanti-reflection layer includes a silicon oxynitride layer.

In one embodiment, the anti-reflection layer has a refractive indexranging between about 2.3 and 3.0. The silicon oxynitride layer is heattreated to increase the refractive index of the silicon oxynitride layerfrom an initial lower amount to an amount ranging between about 2.3 and3.0. The heat treatment is conducted at a temperature greater than about600 C, and for a time duration ranging between about 30 and 360 minutes.

In one embodiment, the photosensitive device comprises a charge-coupleddevice (CCD). The charge-coupled device comprises: a charge transferregion in the substrate adjacent the photosensitive region; and atransfer gate above the transfer region; and the semiconductor imagesensor further comprises: an insulative capping layer on theanti-refection layer; a shielding layer on the capping layer betweenside portions of the anti-reflection layer and the transfer gate; and aplanarization layer on the shielding layer and capping layer.

The device further optionally includes an inner lens formed in theplanarization layer, a microlens on the planarization layer, and/or acolor filter layer on the planarization layer.

In one embodiment, the photosensitive device comprises a CMOS imagesensor (CIS) device. The CMOS image sensor (CIS) device comprises: acharge transfer region in the substrate adjacent the photosensitiveregion; a floating diffusion region adjacent the charge transfer regionopposite the photosensitive region; and a transfer gate above the chargetransfer region; and the semiconductor image sensor further comprises: adielectric layer on the anti-refection layer; metal interconnects in thedielectric layer; and metal vias through the dielectric layer to connectfirst and second metal interconnects with the transfer gate and with thefloating diffusion region respectively. The dielectric layer comprisesmultiple dielectric layers, and the metal interconnects are at topportions of the multiple dielectric layers. The device optionallyfurther includes an inner lens on the dielectric layer, a planarizationlayer on the inner lens and a microlens on the planarization layer,and/or a color filter layer on the planarization layer.

In one embodiment, a hole accumulation layer (HAL) is provided at a topportion of the photosensitive region.

In one embodiment, the anti-reflection layer comprises: a first silicondioxide layer; and a silicon oxynitride layer on the first silicondioxide layer. The silicon oxynitride layer is deposited on the firstsilicon dioxide layer using plasma enhanced chemical vapor deposition(PECVD). The anti-reflection layer may optionally further comprise: asecond silicon dioxide layer on the silicon oxynitride layer; and asilicon nitride layer on the second silicon dioxide layer.

In another aspect, the present invention is directed to a semiconductorimage sensor. The sensor includes a photosensitive device including aphotosensitive region formed in a semiconductor substrate. Ananti-reflection layer is provided proximal to the photosensitive regionfor reducing reflection at a top interface of the photosensitive region.The anti-reflection layer has a refractive index ranging between about2.3 and 3.0.

In one embodiment, the anti-reflection layer includes a siliconoxynitride layer that is heat treated to increase the refractive indexof the silicon oxynitride layer.

In another aspect, the present invention is directed to ananti-reflection layer for use in a semiconductor imaging device. Theanti-reflection layer includes a first silicon dioxide layer and asilicon oxynitride layer on the first silicon dioxide layer. The siliconoxynitride layer is heat treated such that the silicon oxynitride layerhas a refractive index ranging between about 2.3 and 3.0.

In one embodiment, the anti-reflection layer further comprises: a secondsilicon dioxide layer on the silicon oxynitride layer; and a siliconnitride layer on the second silicon dioxide layer.

In another aspect, the present invention is directed to a charge-coupleddevice (CCD) image sensor. The sensor comprises a photosensitive regionformed in a semiconductor substrate. A hole-accumulation layer (HAL) isformed at a top portion of the photosensitive region. A charge transferregion is provided in the substrate adjacent the photosensitive region.A transfer gate is above the transfer region. An anti-reflection layeris above the photosensitive region for reducing reflection at a topinterface of the hole-accumulation layer (HAL). The anti-reflectionlayer includes a silicon oxynitride layer. An insulative capping layeris on the anti-refection layer. A shielding layer is on the cappinglayer between side portions of the anti-reflection layer and thetransfer gate.

In another aspect, the present invention is directed to a CMOS imagesensor (CIS). A photosensitive region is formed in a semiconductorsubstrate. A hole-accumulation layer (HAL). is formed at a top portionof the photosensitive region. A charge transfer region is in thesubstrate adjacent the photosensitive region. A floating diffusionregion is provided adjacent the charge transfer region opposite thephotosensitive region. A transfer gate is above the transfer region. Ananti-reflection layer is above the photosensitive region for reducingreflection at a top interface of the hole-accumulation layer (HAL). Theanti-reflection layer includes a silicon oxynitride layer. A dielectriclayer is on the anti-refection layer. Metal interconnects are providedin the dielectric layer. Metal vias are provided through the dielectriclayer to connect first and second metal interconnects with the transfergate and with the floating diffusion region respectively.

The dielectric layer comprises multiple dielectric layers, and the metalinterconnects are at top portions of the multiple dielectric layers. TheCIS device optionally further includes an inner lens on the dielectriclayer, a planarization layer on the inner lens and a microlens on theplanarization layer, or a color filter layer on the planarization layer.

In another aspect, the present invention is directed to a semiconductorimage sensor. A photosensitive device includes a photosensitive regionformed in a semiconductor substrate. An anti-reflection layer isprovided proximal to the photosensitive region for reducing reflectionat a top interface of the photosensitive region. The anti-reflectionlayer comprises a first silicon dioxide layer; a silicon oxynitridelayer on the first silicon dioxide layer; a second silicon dioxide layeron the silicon oxynitride layer; and a silicon nitride layer on thesecond silicon dioxide layer.

In one embodiment, the silicon oxynitride layer is deposited on thefirst silicon dioxide layer using plasma enhanced chemical vapordeposition (PECVD). The silicon oxynitride layer is heat treated toincrease the refractive index of the silicon oxynitride layer from aninitial lower amount to an amount ranging between about 2.3 and 3.0.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of theinvention will be apparent from the more particular description ofpreferred embodiments of the invention, as illustrated in theaccompanying drawings in which like reference characters refer to thesame parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

FIG. 1 is a sectional view of a conventional imaging device.

FIG. 2 is a sectional close-up view of an anti-reflection layer of theconventional imaging device of FIG. 1.

FIG. 3 is an experimental graph illustrating reflectance as a functionof the wavelength of light as a result of the application ofconventional first and second anti-reflection layers.

FIG. 4 is a conceptual representation of a charge coupled device (CCD).

FIG. 5 is a schematic representation of a CMOS image sensor (CIS).

FIGS. 6A-6F are cross-sectional views of a first embodiment of a processfor forming an image sensor in accordance with the present invention.

FIGS. 7A-7E are cross-sectional views of a second embodiment of aprocess for forming an image sensor in accordance with the presentinvention.

FIGS. 8A-8D are cross-sectional views of a third embodiment of a processfor forming an image sensor in accordance with the present invention.

FIG. 9 is an experimental graph illustrating reflectance as a functionof light wavelength for the first and second embodiments, in accordancewith the present invention.

FIG. 10 is a cross-sectional view of an embodiment of a CMOS imagesensor (CIS) in accordance with the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 4 is a conceptual representation of a charge coupled device (CCD).A CCD comprises an array of photodiode pixels 80 at which photon energyis captured and accumulated. The captured charge is converted toelectrical energy at adjacent vertical buried charge-coupled devices 82,and transferred from the vertical buried charge coupled devices 82 to ahorizontal buried charge coupled device 84. The charge is thentransferred from the horizontal buried charge coupled device 84 throughan output gate OG 86 to a floating diffusion FD unit 88, where thecharge is accumulated. The accumulated charge is periodicallytransferred through a source follower buffer S/F 92 to processingcircuitry. Following transfer, a reset gate RG 90 is activated to drainthe accumulated charge to a reset drain RD. An advantage of the CCDarray lies in that no transmission or signal lines are needed at thepixel level to retrieve the incident energy from the individual pixels.

A CMOS image sensor (CIS), on the other hand, as representedschematically in FIG. 5, includes a plurality of transistors for eachdevice pixel. Each pixel 93 of the array operates as an active pixelsensor (APS), and includes a photo-diode PD, at which the incident lightenergy is captured and converted to electrical energy. A transfer gate94 receives an activation signal via a transfer gate line TG, andtransfers the electrical information received at the photodiode PD to afloating diffusion node FD. A source follower transistor 95 andcorresponding current selection transistor 96, activated by select lineSEL, transfer the energy stored at the floating diffusion node FD to anoutput line 97, and the output analog electrical signal is provided toan analog-to-digital converter ADC 98, where the signal is converted forfurther digital processing. Following a read, the floating diffusionregion FD is reset by reset transistor 99, which is activated by resetline RS. While the CIS array configuration requires that signal lines berouted to the various transistors at each pixel 93, the CISconfiguration offers the advantages of relatively low power consumptionand enhanced circuit integration over the CCD configuration, as the CISconfiguration includes both APS blocks and image signal processingcircuitry in a common chip.

FIGS. 6A-6F are cross-sectional views of a first embodiment of a processfor forming an image sensor in accordance with the present invention. Inthe drawings of FIGS. 6A to 6F, a CCD device image sensor is depicted;however, the principles of the present invention apply equally well toCIS-type image sensors, and other forms of image sensors, and methods offabrication thereof,

FIG. 6A is a cross-sectional view of the CCD device of FIG. 4 takenalong section line A-A. With reference to FIG. 6A, a p type well 101 isformed in a region of a semiconductor substrate 100, for example asilicon-based substrate. The p type well 101 is formed by implantingboron B at an energy level of 3 MeV, and a dopant concentration of2E¹¹/cm². A photon-receiving region 102 is formed in the p type well 101by implanting arsenic As at an energy level of 800 eV, and a dopantconcentration of 2E¹¹/cm². A p+ type channel stop region 110 is formedat a first side of the photon-receiving region 102 by implanting a ptype dopant. A p type transfer region 112 is formed at a second side ofthe photon-receiving region 102 by implanting a p type dopant. Thedoping concentration in the p+ type channel region 110 is higher thanthe doping concentration in the p type transfer region 112.

A p type buffer region 108 is formed at a side of the p type transferregion 112 opposite the photon-receiving region 102 by implanting a ptype dopant. An n type transfer region 106 is formed on the p typebuffer region 108 by implanting n type dopant. A hole accumulation layer(HAL) 104 is formed on the photon-receiving region 102 by implanting a ptype dopant.

During operation, the hole accumulation layer (HAL) 104 operates as aphotodiode to prevent the “dark current effect” from occurring in thephoton-receiving region 102. Under this phenomenon, remanent electronsthat are trapped at the top surface of the substrate or the gatedielectric layer (see FIG. 6B, below) migrate into the photon-receivingregion 102. This causes a false reading of the photon energy, even inthe absence of photon energy incident on the device. The HAL mitigatesor prevents the occurrence of this phenomenon.

Electrons captured at the photon-receiving region 102 migrate to thecorresponding n type transfer region 106, also referred to in the art asthe “charge-coupled device”. The p+ type channel stop region 110operates to provide a potential barrier which prevents electrons frommigrating in a lateral direction from the photon-receiving region 102 tothe n type transfer region 106A that forms a charge-coupled device of anadjacent pixel.

Referring to FIG. 6B, a gate dielectric layer 114′ is provided on theresulting structure. The gate dielectric layer comprises, for example, asilicon dioxide SiO₂ or a SiO₂/Si₂N₃/SiO₂ (ONO) sequentially-stackedlayer.

Referring to FIG. 6C, an electrode layer comprising polysilicon materialand a photoresist layer are next sequentially formed on the gatedielectric layer 114′. The photoresist layer is patterned, and theunderlying layers are etched using the patterned photoresist layer 118as an etch mask to expose the underlying silicon substrate in thephoton-receiving region 102 and the hole accumulation layer (HAL) 104.In this manner, a patterned gate dielectric 114 and an electrode 116 ofa vertical buried charge coupled device (VBCCD) are formed.

Referring to FIG. 6D, the patterned photoresist layer 118 is removed,and a silicon dioxide layer 131 is formed on the resulting structure,including the hole accumulation layer (HAL) 104 on the photon-receivingregion 102. The silicon dioxide layer 131 is formed, for example, usinglow-pressure chemical vapor deposition (LPCVD) or atomic layerdeposition (ALD) to a thickness ranging between about 5-50 nm. Thesilicon dioxide layer 131 operates as a buffer layer to relievemechanical stress between the surface of the HAL region 104 and asubsequent layer to be formed on the silicon dioxide layer 131, and alsoprevents surface degradation of the HAL region 104 during subsequentfabrication processes, which is important for minimizing the darkcurrent effect. The refractive index n1 and the thickness of the silicondioxide layer 131 are respectively on the order of about 1.4-1.5 andabout 5-50 nm.

Referring to FIG. 6E, a silicon oxynitride (Si_(x)O_(y)N_(z), or SiON)layer 133 is next uniformly deposited on the silicon dioxide layer 131.The silicon oxynitride layer 133 is formed by plasma enhanced chemicalvapor deposition (PECVD) using silane (SiH₄), NH₃, N₂O, and N₂ gases. Atthe time of deposit, the silicon oxynitride layer 133 has a refractiveindex value of about 2.0. The silicon oxynitride layer 133 is then heattreated or annealed at a temperature greater than 600 C for about 30-360minutes in an inert gas environment. The thickness of the resultingsilicon oxynitride layer 133 is on the order of about 20-60 nm. The heattreatment may be applied immediately following deposit of the siliconoxynitride layer 133, or, optionally, may be applied during processingof subsequent device layers.

As a result of the above heat treatment, the refractive index n2 of thesilicon oxynitride layer 133 is increased from about 2.0 to about2.3-3.0, preferably to 2.4-2.6. The refractive index n3 of the holeaccumulation layer 104 is about 4.5. The refractive index of a materiallayer has a direct effect on the resulting reflectivity of the layer, inaddition to other factors such as layer thickness and the like. Therefractive indices of adjacent layers should be matched as closely aspossible to ensure minimization of reflection at their interface.Together, the silicon dioxide layer 131 and silicon oxynitride layer 133operate as an anti-reflection layer for the imaging device of thepresent invention. Formation of the silicon oxynitride layer 133 byPECVD is preferred as it has been demonstrated that the properties ofthe silicon oxynitride layer deposited in this manner are such that therefractive index of the layer can be raised from a value about 2.0,initially after deposit, to a value in the range of 2.3-3.0, followingthe heat treatment. Raising the value of the refractive index decreasesthe resulting reflectivity of the layer. Such an ability to increase therefractive index following heat treatment was found experimentally to beabsent in a silicon oxynitride layer deposited using low-pressurechemical vapor deposition (LPCVD).

With reference to FIG. 6F, the silicon oxynitride layer 133 of theanti-reflection layer 130 is patterned in a region above thephoton-receiving region 102. A capping layer 150, comprising for examplesilicon dioxide SiO₂, is formed on the resulting structure including thepatterned anti-reflection layer 130. A dielectric layer 157 such as SiO₂or Si₃N₄ is formed on the resulting structure. A shielding layer 152 isthen formed on the resulting structure, and the shielding layer 152 ispatterned to expose the capping layer 150 above the patternedanti-reflection layer 130. Following this, a planarization layer 154comprising silicon dioxide SiO₂, or resin, is formed, and a lens 156comprising resin is formed on the resulting structure according toconventional techniques. An optional inner lens structure 153 comprisingSiO₂, Si₃N₄, or resin may be formed in the planarization layer 154, forexample according to the techniques disclosed in U.S. Pat. Nos.6,614,479 and 6,030,852, incorporated herein by reference, for thepurpose of improving the focusing of incident photons into thephoton-receiving region 102. The resulting indices of refraction of thevarious layers are as follows: hole accumulation layer 104—4.5; silicondioxide layer 131—1.45; silicon oxynitride layer 133—2.5; capping layer150—2.0; and planarization layer 154—1.5.

In this manner, the silicon oxynitride layer 133 is deposited, and, as aresult of the above-described heat treatment, the refractive index ofthe silicon oxynitride layer 133 is raised to a level that is greaterthan that of the conventional silicon nitride layer, which has arefractive index of about 2. This results in a decrease in reflectivityof the resulting anti-reflection layer 130 including the siliconoxynitride layer 133, in turn resulting in improved photon capture andmore efficient optical-to-electrical energy transfer at the pixel level.

FIGS. 7A-7E are cross-sectional views of a second embodiment of aprocess for forming an image sensor in accordance with the presentinvention.

FIG. 7A is a cross-sectional view of the CCD device of FIG. 4 takenalong section line A-A in accordance with a second embodiment of thepresent invention. In the same manner as the embodiment shown in FIG.6E, the solid state imaging device of FIG. 7A includes a first silicondioxide layer 131 and a first silicon oxynitride layer 133. However,prior to patterning of the silicon oxynitride layer 133 as shown in FIG.6F of the first embodiment, the present second embodiment includes asecond silicon dioxide layer 141 and a silicon nitride layer 143 thatare sequentially formed on the silicon oxynitride layer 133. Therefore,in this embodiment, the anti-reflection layer 140 includes the firstsilicon dioxide layer 131, the silicon oxynitride layer 133, the secondsilicon dioxide layer 141, and the silicon nitride layer 143, appliedsequentially. As in the first embodiment, the first silicon dioxidelayer 131 of the second embodiment is formed, for example usinglow-pressure chemical vapor deposition (LPCVD) or atomic layerdeposition (ALD) to a thickness ranging between about 5-50 nm. Thesilicon oxynitride layer 133 is formed by plasma enhanced chemical vapordeposition (PECVD), as described above to a thickness of about 20-60 nm.The second silicon dioxide layer 141 is applied by chemical vapordeposition (CVD) to a thickness of about 10-70 nm. The silicon nitridelayer 143 is deposited on the resulting structure to a thickness ofabout 5-35 nm using a CVD process that uses source gases of SiH₄, N₂O,and/or NH₃ in an environment of nitrogen. As described above, thesilicon oxynitride layer 133 is heat-treated at a temperature greaterthan 600 C for about 30-360 minutes in an inert gas environment. Theheat treatment may be applied immediately following deposit of thesilicon oxynitride layer 133, or during or following the deposit ofsubsequent layers, as described above. As a result of the heattreatment, the refractive index n2 of the silicon oxynitride layer 133is increased from about 2.0 at the time of deposit to about 2.3-3.0,preferably to 2.4-2.6. The resulting refractive indices of the variouslayers are as follows: first silicon dioxide layer 131—1.4 to 1.5;silicon oxynitride layer 133, 2.3-3.0, preferably 2.4-2.6; secondsilicon dioxide layer 141, 1.4-1.5; and silicon nitride layer 143,1.9-2.1.

Application of the second anti-reflection layer, comprising the secondsilicon dioxide layer 141 and the silicon nitride layer 143, operates tofurther reduce the reflectivity at the top surface of the substrate. Anexperimental example of the results obtained is provided below inconjunction with FIG. 9.

Referring to FIG. 7B, the resulting structure is coated with aphotoresist layer that is patterned to form a photoresist pattern 190 onthe anti-reflection layer 140 above the photon-receiving region 102 ofthe device. The photoresist pattern 190 is used to etch the underlyinganti-reflection layer 140. A dry etch or wet etch process may be appliedto remove the anti-reflection layer 140. In the wet-etch process, asolution of H₃PO₄ may be used for etching of the silicon nitride layer143. A solution of HF may be used for etching of the second silicondioxide layer 141, and the solution of HF may be used for etching of thesilicon oxynitride layer 133.

Referring to FIG. 7C, following the etch, the patterned anti-reflectionlayer 140′ comprises a patterned silicon nitride layer 143′, a patternedsecond silicon dioxide layer 141′, a patterned silicon oxynitride layer133′, and the first silicon dioxide layer 131. The first silicon dioxidelayer 131 remains intact during the etch process to serve as aprotection layer to prevent surface damage to the hole accumulationlayer (HAL) 104. Since the hole accumulation layer (HAL) 104 has arefractive index of about 4.5, the multiple layers of theanti-reflection layer 140′ operate to gradually transition the change inrefractive index between the hole accumulation layer 104 and upperlayers, to thereby minimize reflectivity at the top surface of thephoton-receiving region 102.

Referring to FIG. 7D, a capping layer 150, for example comprisingsilicon dioxide, is deposited using CVD on the anti-reflection layer140′.

FIG. 7E is a cross-sectional illustration of the resulting solid-stateimaging device. A shielding layer 152 comprising W or Al is applied tothe resulting structure, as described above, for preventing photons fromdirectly entering the vertical buried charge coupled device (VBCCD) 116.A planarization layer 154, for example comprising a transparent resin ora silicon dioxide layer is formed using a coating technique, and thenplanarized for serving as a base for the microlens 156. A microlenslayer is formed for example of resin on the planarization layer 154, andthen microlenses 156 are formed according to conventional techniques. Anoptional color filter 155 may be inserted between the planarizationlayer 154 and the microlens 156. In one embodiment, the color filter 155layer comprises a photoresist material layer having a color pigment. Thecolor filter 155 may likewise be applied to the embodiment shown anddescribed above with reference to FIG. 6F. In addition, an optionalinner lens 153 may be provided in the planarization layer 154, asdescribed above.

FIGS. 8A-8D are cross-sectional views of a third embodiment of a processfor forming an image sensor in accordance with the present invention

FIG. 8A is a cross-sectional illustration of a solid state imagingdevice having a multiple layered anti-reflection layer 140 applied in amanner similar to that described above with reference to FIG. 7A. Inthis embodiment, a hard mask 200, for example comprising silicondioxide, is layered on the anti-reflection layer 140.

Referring to FIG. 8B, the hard mask 200 is patterned to form a patternedhard mask 200′ according to conventional photolithographic techniques ina region above the photon-receiving region 102 as shown.

Referring to FIG. 8C, the silicon nitride layer 143′ is etched in a wetetch process using phosphoric acid (H₃PO₄) as an etch solution.

Referring to FIG. 8D, the second silicon dioxide layer 141′ and thesilicon oxynitride layer 133′ are subsequently etched using a wetetching process utilizing hydrofluoric acid (HF) as an etch solution. Inthis manner, the anti-reflection layer 140′ is patterned using apatterned hard mask 200′ as an etch mask. Following this, subsequentlayers are applied, as shown above in FIGS. 6F and 7E, for furtherfabrication of the device.

FIG. 9 is an experimental graph illustrating reflectance as a functionof light wavelength for the first, second, and third embodimentsrespectively including the anti-reflection layers of the presentinvention. In this graph it can be seen that as a result of the presenceof the first anti-reflection layer 130, charted by graph 202, there is asignificant decrease in resulting reflectance over a majority of theband of wavelengths between about 400-700 nm, as compared to theconventional embodiments the experimental results for which are graphedin FIG. 3 above. In the second and third embodiments of the presentinvention, which include multiple anti-reflection layers 140′ thatincludes multiple layers, an even further improvement in resultingreflectance is demonstrated over a majority of the band of wavelengths.The above embodiments depicted in FIGS. 6, 7 and 8 are described abovein conjunction with a charge-coupled device (CCD)-type image sensors.However, the principles of the present invention are equally applicableto other forms of image sensors such as CMOS image sensors (CIS).Application of the present invention to a CIS-type device will now bedescribed with reference to FIG. 10.

FIG. 10 is a cross-sectional view of an embodiment of a CMOS imagesensor (CIS) in accordance with the present invention. In the embodimentof FIG. 10, a p type epitaxial layer 212 is formed on a semiconductorsubstrate 210. A p well region 214 is formed in a top portion of thesubstrate 210. Shallow trench isolation structures 220 are formed asshown and define an active region 221 therebetween.

An n type photodiode device (PD) region 216 is formed at one side of theactive region, and an optional p type hole accumulation layer (HAL)region 218 is formed at a top portion of the photodiode device region216. A p type transfer region 224 is provided adjacent the photodiodedevice region 216, and an n+ floating diffusion (FD) region 226 isformed adjacent the transfer region 224 opposite the photodiode deviceregion 216. An anti-reflection layer 266 comprising a silicon dioxidelayer 264 and silicon oxynitride layer 262 are formed on the holeaccumulation layer 218 as described above. The silicon oxynitride layeris heat-treated, as described above, either immediately following itsapplication, or during subsequent processing, in order to increase theindex of refraction of the layer to a desired level, as described above.The anti-reflection layer 266 may comprise a layer configured inaccordance with the first embodiment shown above in FIG. 6F, or maycomprise a layer configured in accordance with the second or thirdembodiments of FIG. 7E or FIG. 8D, as described above. The siliconoxynitride layer 262 is formed by plasma enhanced chemical vapordeposition (PECVD) as described above, such that the refractive index ofthe material can be increased during the subsequent heat treatment.

A transfer gate oxide 228 and transfer gate metal 230 are formed on thetransfer gate 224. A multiple-layered interlayer dielectric 236 isformed over the resulting structure, and an inter-layer vias 232, forexample comprising tungsten or copper vias, are formed through theinterlayer dielectric in order to make contact with the transfer gate230 and the floating diffusion region 226 as shown. Metal interconnects,for example comprising aluminum or copper 234, are formed on theinterlayer vias 232 and at other vertical positions above the resultingstructure. Multiple intermetal dielectric layers are subsequentlyformed, each layer having corresponding metal interconnects 234 andinter-layer vias 232 for routing electronic signals from the transfergate 230 and the floating diffusion region 226 and for routing otherdevice signals. The metal interconnects 234 are laterally positioned soas not to interfere with the introduction of light into the photodiodedevice region 216. Metal interconnects 234A formed on a top layer of theinterlayer dielectric 236 are coated with a buffer layer 238 comprisingsilicon nitride, silicon dioxide, or silicon oxynitride.

An optional inner lens 240 comprising silicon nitride is formed on thebuffer layer along the incident light path. The inner lens 240 is formedin one example by first forming a silicon nitride layer on theunderlying interlayer dielectric 236 and metal interconnects 234A. Aphotoresist layer is formed on the silicon nitride layer, and thephotoresist layer is patterned to form a photoresist structure. Thephotoresist structure is re-flowed to have a lens-type curvature and thesilicon nitride layer is etched back using the curved reflowedphotoresist structure as an etch mask. In this manner, a similarlycurved silicon nitride inner lens 240 is formed.

A first planarization layer comprising resin is formed on the resultingstructure and is planarized. An optional color filter 244 is formed onthe first planarization layer 258, and a second planarization layer 246,for example comprising resin, is formed on the color filter 244, andplanarized. A microlens 250 comprising resin is formed on the secondplanarization layer 246 as described above. In the CIS embodiment, thesize of the resulting pixels is reduced and the number of pixelsincreased, such that the CIS embodiment enjoys application in compactsystems such as mobile telephones that include cameras. However, as aconsequence of the relatively small size of the pixel, the photodiodereceives less light energy. The antireflection layer of the presentinvention improves the efficiency of light transfer in theseapplications.

As in the CCD example of FIGS. 6, 7, and 8 above, the application of thesilicon oxynitride layer 262 to the CIS embodiment of FIG. 10, and thesubsequent heat treatment of the silicon oxynitride layer 262 results ina layer having a refractive index on the order of about 2.3-3.0,preferably about 2.4-2.6. Formation of the silicon oxynitride layer 262using PECVD is preferred, since the properties of the material depositedin this matter are such that the refractive index can be raised from aninitial value of about 2.0 following deposit to a value in the range of2.3-3.0 following the heat treatment. This higher index of refraction inthe anti-reflection layer 266 results in reduced reflectivity at theupper surface of the photodiode device (PD) 216 region of the device,which can have a relatively high index of refraction at about 4.5, ascompared to the relative low indices of refraction of the upper layer ofthe device, including the microlens 250 (n=1.6), first and secondplanarization layers 246, 258 (n=1.6), color filter 244 (n=1.6), innerlens 240 (n=2.0) and interlayer dielectric layers 236 (n=1.5). Asdescribed above, a large difference in index of refraction at thejunction of two different materials can cause increased reflectivity atthat junction. The oxynitride antireflection layer 262 of the presentinvention avoids this problem by serving as a transition layer betweenthe relatively high index of refraction photodiode layer in thesemiconductor substrate, and the relatively low index of refraction inthe interlayer dielectric 236, and upper layers of the device. Thereduced reflectivity at this junction promotes increased transfer ofphotons into the photodiode device region 216 of the CIS, which is animportant consideration as the trend of ever-increasing deviceintegration continues.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and detail may bemade herein without departing from the spirit and scope of the inventionas defined by the appended claims.

For example, the present invention is applicable to use with any type ofphotosensitive device, including photodiodes, phototransistors,photogates, pinned photodiodes, threshold-voltage-modulated MOSFETs,avalanche diodes, Schottky diodes, p-i-n diodes back-side illuminationdevices, quantum well devices, and the like. In addition, while thepresent specification describes in detail one form of CIS pixel device,with reference to FIG. 5, that utilizes five transistors, the presentinvention is equally applicable to other CIS pixel structures, forexample including the three-transistor structure, four transistorstructure, five transistor structure, the photogate structure, and otherCIS imaging device structures well known to those in the art ofsemiconductor imaging devices.

1. A method of forming an imaging device comprising: forming aphotosensitive device in a semiconductor substrate, the photosensitivedevice including a photosensitive region; forming an anti-reflectionlayer on the photosensitive region; the anti-reflection layer comprisinga silicon oxynitride layer; and heat treating the silicon oxynitridelayer to increase a refractive index of the silicon oxynitride layer. 2.The method of claim 1 wherein forming a photosensitive device comprisesforming a charge-coupled device (CCD).
 3. The method of claim 2 whereinforming a charge-coupled device comprises: forming a charge transferregion in the substrate adjacent the photosensitive region; and forminga transfer gate above the transfer region; and further comprising:forming an insulative capping layer on the anti-refection layer; forminga shielding layer on the capping layer between side portions of theanti-reflection layer and the transfer gate; and forming a planarizationlayer on the shielding layer and capping layer.
 4. The method of claim 3further comprising forming an inner lens in the planarization layer. 5.The method of claim 1 wherein forming a photosensitive device comprisesforming a CMOS image sensor (CIS) device.
 6. The method of claim 5wherein forming a CMOS image sensor (CIS) device comprises: forming afloating diffusion region adjacent a charge transfer region opposite thephotosensitive region; and forming a transfer gate on the chargetransfer region.
 7. The method of claim 6 further comprising: forming adielectric layer on the anti-reflection layer; and forming metalinterconnects in the dielectric layer.
 8. The method of claim 6 furthercomprising forming an inner lens on the dielectric layer.
 9. The methodof claim 6 further comprising forming a planarization layer on the innerlens and forming a microlens on the planarization layer.
 10. The methodof claim 9 further comprising forming a color filter layer on theplanarization layer.
 11. The method of claim 1 wherein forming aphotosensitive device further comprises forming a hole accumulationlayer (HAL) at a top portion of the photosensitive region.
 12. Themethod of claim 1 wherein forming the anti-reflection layer comprises:forming a first silicon dioxide layer on the photosensitive region; andforming the silicon oxynitride layer on the first silicon dioxide layer.13. The method of claim 12 wherein forming the first silicon dioxidelayer comprises depositing the first silicon dioxide layer on thephotosensitive region using one of a low pressure chemical vapordeposition (LPCVD) process and an Atomic Layer Deposition (ALD) process.14. The method of claim 12 wherein forming the silicon oxynitride layercomprises depositing the silicon oxynitride layer on the first silicondioxide layer using plasma enhanced chemical vapor deposition (PECVD).15. The method of claim 14 wherein forming the silicon oxynitride layercomprises depositing the silicon oxynitride layer using plasma enhancedchemical vapor deposition (PECVD) to a thickness of about 20 to 60 nm.16. The method of claim 12 wherein forming the anti-reflection layerfurther comprises: forming a second silicon dioxide layer on the siliconoxynitride layer; and forming a silicon nitride layer on the secondsilicon dioxide layer.
 17. The method of claim 16 wherein forming thesecond silicon dioxide layer comprises depositing the second silicondioxide layer on the photosensitive region using a chemical vapordeposition (CVD) process.
 18. The method of claim 12 wherein heattreating the silicon oxynitride layer increases the refractive index ofthe silicon oxynitride layer to an amount ranging between about 2.3 and3.0.
 19. The method of claim 1 further comprising patterning theanti-reflection layer in a region above the photosensitive layer. 20.The method of claim 19 wherein patterning the anti-reflection layercomprises: providing a photoresist layer on the anti-reflection layer;patterning the photoresist layer above the photosensitive region; andremoving the silicon oxynitride layer of the anti-reflection layer usingthe patterned photoresist layer as a mask.
 21. The method of claim 19wherein patterning the anti-reflection layer comprises: providing a hardmask layer on the anti-reflection layer; patterning the hard mask layerabove the photosensitive region; and removing the silicon oxynitridelayer of the anti-reflection layer using the patterned hard mask layeras a mask.
 22. The method of claim 21 wherein removing the siliconoxynitride layer of the anti-reflection layer comprises removing thesilicon oxynitride layer using an HF solution.
 23. The method of claim 1wherein forming the anti-reflection layer comprising the siliconoxynitride layer comprises forming the silicon oxynitride layer usingplasma-based chemical vapor deposition (CVD).
 24. The method of claim 23wherein the plasma-based chemical vapor deposition comprises plasmaenhanced chemical vapor deposition (PECVD).
 25. The method of claim 24wherein heat treating the silicon oxynitride layer increases therefractive index of the silicon oxynitride layer to an amount rangingbetween about 2.3 and 3.0.
 26. The method of claim 1 wherein heattreating the silicon oxynitride layer increases the refractive index ofthe silicon oxynitride layer to an amount ranging between about 2.3 and3.0.
 27. The method of claim 1 wherein heat treating the siliconoxynitride layer is performed immediately following formation of thesilicon oxynitride layer.
 28. The method of claim 1 wherein heattreating the silicon oxynitride layer is performed during furtherprocessing of the imaging device.
 29. A method of forming an imagingdevice, comprising: forming a photosensitive device in a semiconductorsubstrate, the photosensitive device including a photosensitive region;and forming an anti-reflection layer on the photosensitive region thatreduces the reflectivity of photon energy at the photosensitive device,the anti-reflection layer including a silicon oxynitride layer; theanti-reflection layer having a refractive index ranging between about2.3 and 3.0.
 30. The method of claim 29 wherein forming ananti-reflection layer comprises: forming the anti-reflection layerproximal to the photosensitive device so that the anti reflection layerhas a refractive index of about 2.0; and heat treating the siliconoxynitride layer to increase the refractive index of the siliconoxynitride layer to range between about 2.3 and 3.0.
 31. The method ofclaim 29 wherein forming the anti-reflection layer comprises: forming afirst silicon dioxide layer on the photosensitive region; and formingthe silicon oxynitride layer on the first silicon dioxide layer.
 32. Themethod of claim 31 wherein forming the silicon oxynitride layercomprises depositing the silicon oxynitride layer on the first silicondioxide layer using plasma enhanced chemical vapor deposition (PECVD).33. The method of claim 31 wherein forming the anti-reflection layerfurther comprises: forming a second silicon dioxide layer on the siliconoxynitride layer; forming a silicon nitride layer on the second silicondioxide layer.
 34. The method of claim 29 wherein forming theanti-reflection layer comprising the silicon oxynitride layer comprisesforming the silicon oxynitride layer using plasma-based chemical vapordeposition (CVD).
 35. The method of claim 34 wherein the plasma-basedchemical vapor deposition comprises plasma enhanced chemical vapordeposition (PECVD).
 36. A method of forming a semiconductor imagesensor, comprising: forming a photosensitive device including aphotosensitive region in a semiconductor substrate; and forming ananti-reflection layer on and proximal to the photosensitive region forreducing reflection at a top interface of the photosensitive region, theanti-reflection layer including a silicon oxynitride layer, whereinforming the anti-reflection layer comprises forming the anti-reflectionlayer to have a refractive index ranging between about 2.3 and 3.0. 37.The method of claim 36 wherein forming the anti-reflection layercomprises: forming the anti-reflection layer proximal to thephotosensitive device so that the anti reflection layer has a refractiveindex of about 2.0; and heat treating the silicon oxynitride layer toincrease the refractive index of the silicon oxynitride layer to rangebetween about 2.3 and 3.0.
 38. The method of claim 37 wherein heattreating the silicon oxynitride layer comprises heat treating at atemperature greater than about 600 C.
 39. The method of claim 38 whereinheat treating the silicon oxynitride layer comprises heat treating for atime duration ranging between about 30 and 360 minutes.
 40. The methodof claim 36 wherein forming the anti-reflection layer comprises: forminga first silicon dioxide layer on the photosensitive region; and formingthe silicon oxynitride layer on the first silicon dioxide layer.
 41. Themethod of claim 40 wherein forming the anti-reflection layer furthercomprises: forming a second silicon dioxide layer on the siliconoxynitride layer; and forming a silicon nitride layer on the secondsilicon dioxide layer.
 42. The method of claim 36 wherein forming thesilicon oxynitride layer comprises depositing the silicon oxynitridelayer on the first silicon dioxide layer using plasma enhanced chemicalvapor deposition (PECVD).
 43. A semiconductor image sensor, comprising:a photosensitive device including a photosensitive region formed in asemiconductor substrate; and an anti-reflection layer proximal to thephotosensitive region for reducing reflection at a top interface of thephotosensitive region, the anti-reflection layer including a siliconoxynitride layer, the anti-reflection layer having a refractive indexranging between about 2.3 and 3.0.